1. Technical Field
The present invention relates generally to a transmission system, and in particular, to a transmission system capable of providing both a data service and a voice service.
2. Related Art
An x-digital subscriber line (xDSL) technique is typically used to provide a high-speed data service using an existing telephone line. The xDSL chiefly includes asymmetrical digital subscriber line (ADSL), universal asymmetrical digital subscriber line (UADSL), high bit rate digital subscriber line (HDSL), symmetrical digital subscriber line (SDSL), multi-rate symmetrical digital subscriber line (MSDSL), rate adaptive digital subscriber line (RADSL), very high digital subscriber line (VDSL), and also IDSL (ISDN like DSL) wherein ISDN is integrated services digital network.
ADSL supports both a high-speed data service and a standard voice service through a twisted pair copper line. The ADSL is advantageous in that it is currently widespread and supports a high downstream rate of up to 7 megabits per second (Mbps). However, the ADSL is disadvantageous in that its upstream rate is limited to a maximum of 800 kilobits per second (Kbps).
The high bit rate digital subscriber line (HDSL) is a preliminary technique for an alternative proposal of T1 (1.544 Mbps) and E1 (2.048 Mbps), which uses 2 twisted pair lines, and is advantageous in that it supports a maximum sync rate of T1 and E1, and it has no repeater between a subscriber and a telephone exchange. However, the HDSL is disadvantageous in that it does not support the standard telephone service and the variable rate, and its downstream rate is limited to the E1 class.
The multi-rate symmetrical digital subscriber line (MSDSL) is a preliminary technique for an alternative proposal of T1 and E1, which uses 1 twisted pair line, and is equal to the HDSL except that it provides the variable rate. The MSDSL is advantageous in that it has somewhat eased distance requirements at the low rate. However, the MSDSL is disadvantageous in that it cannot support the standard telephone service.
More specifically, the multi-rate symmetrical digital subscriber line (MSDSL), a descendant of the symmetrical digital subscriber line (SDSL), is a full duplex sync technique operating at a rate of below E1 or T1, using a single circuit pair, and is distinguishable from the HDSL or the HDSL2 (HDSL version 2) in that it can support several data rates. For example, the MSDSL supports a variable rate of between 128 Kbps and 1920 Kbps. The MSDSL employs a two binary, one quaternary (2B1Q) circuit modulation/demodulation technique, which has high noise immunity.
More specifically describing the HDSL, the HDSL supports a fixed rate (that is, does not support a variable rate). Therefore, the HDSL operates in a T1/E1 full duplex mode, and thus, requires a 2-pair line or 3-pair line. The HDSL or the HDSL2 can support only the high data rate (for example, over the rate of the T1 class). For the circuit modulation/demodulation technique of the HDSL and HDSL2, a carrierless amplitude phase (CAP) technique and the 2B1Q technique are used both, but the two binary, one quarternary (2B1Q) technique is chiefly used. The CAP technique is advantageous in that it has a relatively longer service distance as compared with the 2B1Q technique, while the 2B1Q technique is advantageous in that it has high noise immunity though it has a shorter service distance as compared with the CAP technique. The 2B1Q technique uses the same band for both the upstream and downstream signals, and modulates 2 binary signals into 1 quaternary signal. The 2B1Q technique is used not only for the HDSL but also for the IDSL and SDSL. The carrierless amplitude phase (CAP) technique, which is a quadrature amplifier modulation-based modulation/demodulation technique, is used for SDSL, ADSL and RADSL as well as HDSL. The quadrature amplifier modulation is represented by the acronym QAM.
Meanwhile, since the existing multi-rate symmetrical digital subscriber line (MSDSL) can support only the data service, a separate card capable of supporting the voice service must be provided in order to receive the voice service. The MSDSL is advantageous in that it can provide the data service using 1 twisted pair copper line (that is, existing telephone line), but it is disadvantageous in that the separate card, as stated above, is required to be provided with the voice service (or standard telephone service). In addition, for the voice service, there must be separately provided a splitter and a voice service line interposed between the splitter and the user terminal.
The widespread integrated services digital network (ISDN) service is so developed as to provide both the voice service and the data service, but it supports a low data rate of 128 Kbps, having the limited service quality. In addition, the exchange must process messages exchanged between a network terminal (NT) and the exchange itself, which increases a load on the exchange.
In the meantime, the ADSL can transmit the voice and data signals by mixing them using a discrete multi-tone (DMT) technique. In this case, the voice signal is split from the mixed signal by a splitter in the final stage. The DMT technique for the ADSL is disadvantageous in that a separate splitter must be provided to split the voice signal as in the MSDSL.
As described above, since the digital subscriber line technique such as ADSL, HDSL and MSDSL can support only the high-speed data service (excluding the standard telephone service), a separate device must be installed to support the voice service. In addition, when the user installs the separate device and subscribes to both the high-speed data-class service (hereinafter referred to as a high-speed data service) and the voice-class service (hereinafter referred to as a voice service), a separate line must be additionally installed. Therefore, in view of the financial aspect of the client, it is actually difficult to universalize such a technique.
I have found that methods for providing data services and voice services can be difficult, costly, inefficient, and inconvenient to implement. Efforts have been made to improve data and voice services.
Exemplars of recent efforts in the art include: U.S. Pat. No. 5,978,390 to Balatoni, entitled DUAL DDS DATA MULTIPLEXER, issued on Nov. 2, 1999, U.S. Pat. No. 6,137,866 to Staber et al., entitled INDOOR XDSL SPLITTER ASSEMBLY, issued on Oct. 24, 2000, U.S. Pat. No. 6,144,659 to Nye et al., entitled TELECOMMUNICATION EQUIPMENT SUPPORT OF HIGH SPEED DATA SERVICES, issued on Nov. 7, 2000, U.S. Pat. No. 6,141,356 to Gorman, entitled SYSTEM AND METHOD FOR DISTRIBUTING VOICE AND DATA INFORMATION OVER WIRELESS AND WIRELINE NETWORKS, issued on Oct. 31, 2000, U.S. Pat. No. 6,192,109 to Amrany et al., entitled APPARATUS AND METHOD FOR IMPROVED DSL COMMUNICATION, issued on Feb. 20, 2001, U.S. Pat. No. 5,910,970 to Lu, entitled MDSL HOST INTERFACE REQUIREMENT SPECIFICATION, issued on Jun. 8, 1999, U.S. Pat. No. 6,021,158 to Schurr et al., entitled HYBRID WIRELESS WIRE-LINE NETWORK INTEGRATION AND MANAGEMENT, issued on Feb. 1, 2000, U.S. Pat. No. 6,021,167 to Wu, entitled FAST EQUALIZER TRAINING AND FRAME SYNCHRONIZATION ALGORITHMS FOR DISCRETE MULTI-TONE (DMT) SYSTEM, issued on Feb. 1, 2000, and U.S. Pat. No. 6,044,107 to Gatherer et al., entitled METHOD FOR INTEROPERABILITY OF A TIE 1.4 COMPLIANT ADSL MODEM AND A SIMPLER MODEM, issued on Mar. 28, 2000.
While these recent efforts provide advantages, I note that they fail to adequately provide a method for efficiently and conveniently providing data and voice services.